Adhesives used in the electronic packaging industry typically contain a thermosetting resin combined with a filler and some type of curing initiator. These resins are primarily used in the electronics industry for the preparation of non-hermetic electronic packages. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components. Examples of such packages are ball grid array (BGA) assemblies, super ball grid arrays, IC memory cards, chip carriers, hybrid circuits, chip-on-board, multi-chip modules, pin grid arrays, and the like. For all these applications, the microelectronics industry continues to require new resins that are able to meet its varying demands.
Monomer components used in adhesive die attach paste compositions tend to bleed out onto the substrate during cure, and even (in some cases) during room temperature staging of the adhesive. Indeed, resin bleed can be a serious problem in die attach electronic packaging applications. “Bleed” is defined herein as separation of the monomer vehicle phase and filler during staging or cure, resulting in the spread of resin away from the die bond area. Resin bleed can generate wire bond non-sticks if it flows up onto bonding pads of the microelectronic device itself or the package into which it has been placed.
There are several potential consequences that arise due to resin bleed, e.g., a package assembler must deal with the likelihood of reduced product yields (and the attendant increased costs for manufacture), the part-to-part variability of the bleed phenomenon results in unacceptable part-to-part variability of the desired product, thereby necessitating the additional expense of 100% visual inspection of each component before being passed onto the wire bond step, and the like.
U.S. Pat. No. 4,483,898 discloses the use of alcohols, amides, amines, carboxylic acids, and esters containing two to twelve carbon atoms as being effective for the reduction of spreading of liquid films on substrates, specifically in inhibition of resin bleed for epoxy, acrylate and silicone adhesive systems. The preferred bleed inhibiting compounds were poly-fluorinated (i.e. where most or all of the hydrogens of the hydrocarbon residue had been replaced by fluorine). The effective range contemplated by this patent is 0.05 to 5% by weight of the liquid phase. It is interesting to note, however, that the bleed control failed at 0.2% by weight of the most preferred bleed inhibiting agent in the absence of any “coupling agent” (cf. example VII). Furthermore, several of the compounds disclosed had deleterious effects on the pot life of the epoxy systems in which they were used. Another serious concern connected to the previously disclosed anti-bleed additives is their potential human and environmental toxicity. Poly-fluorinated hydrocarbons, with more than about four carbons in the backbone, are known to bio-accumulate (i.e. to become concentrated in living organisms, and no naturally occurring biological mechanisms exist that can eliminate these compounds from the body once they are absorbed). These materials, therefore, are considered to pose a risk to personal health as well as to the environment.
Accordingly, there remains a need to develop environmentally friendly compounds, compositions and methods useful for reducing the occurrence of resin bleed when die-attach compositions are applied to a substrate.